U.S. patent number 5,159,517 [Application Number 07/554,714] was granted by the patent office on 1992-10-27 for immersion detection circuit interrupter.
This patent grant is currently assigned to Innovative Designer Products, Inc.. Invention is credited to Lawrence E. Bodkin.
United States Patent |
5,159,517 |
Bodkin |
October 27, 1992 |
Immersion detection circuit interrupter
Abstract
A sensing conductor and a detection circuit cause a low
resistance shorting of an appliance circuit in response to
immersion in water or other electrically conductive liquid, and an
interrupter device, preferably located in the plug of the cord set,
reacts to overcurrent, by opening both sides of the line. The
sensing conductor must be strategically placed, within the
appliance housing, to pass in proximity to liquid access points and
the current carrying parts of the appliance. The detection circuit
may be within the appliance or in the plug, with the sensing
conductor extended to the appliance as a third conductor in the
line cord. When a small current passes between the sensing
conductor and the ungrounded or grounded neutral sides of the line
or earth ground, current is shunted through the detection circuit
from the ungrounded to the grounded neutral conductor, and away
from the appliance circuit. A fuse link is opened in one side of
the line which, in turn, releases normally open contacts, in the
other side of the line, which open and remain open, so that both
sides are permanently interrupted.
Inventors: |
Bodkin; Lawrence E.
(Jacksonville, FL) |
Assignee: |
Innovative Designer Products,
Inc. (Kendall Park, NJ)
|
Family
ID: |
24214419 |
Appl.
No.: |
07/554,714 |
Filed: |
July 17, 1990 |
Current U.S.
Class: |
361/49; 307/326;
361/50; 361/58 |
Current CPC
Class: |
H02H
5/083 (20130101) |
Current International
Class: |
H02H
5/00 (20060101); H02H 5/08 (20060101); H02H
003/16 () |
Field of
Search: |
;361/49,50,104,42
;307/116,118,326 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: DeBoer; Todd E.
Attorney, Agent or Firm: Yeager; Arthur G.
Claims
What is claimed as new and what is desired to be secured by Letters
Patent of the United States is:
1. In a power circuit for supplying electrical power from a source
through at lest a pair of conductors to utilization quipment and
including an overcurrent responsive circuit interruption means, the
improvement wherein said interruption means includes a fuse link
and an electrically conductive spring, said fuse link and spring
being physically and electrically connected through at least one
common connection point with said fuse link and spring being in
series with one of said one conductor to conduct electrical power
from a source through said conductors to utilization equipment,
electrical means in series with another of said conductors to
interrupt electrical power from said source through said another
conductor, said fuse link being physically connected to and
electrically isolated from said electrical means to maintain
electrical conduction through said another conductor until said
fuse link is opened by overcurrent, said fuse link interrupting
conduction through said one conductor and causing interruption of
conduction through said electrical means in series with said
another conductor.
2. In a power circuit for supplying electrical power from at least
two conductors to an appliance circuit having an electrical shock
protection device including an immersion sensing conductor in a
housing of an appliance which is connected to a detection circuit
including a current interruption mechanism controlled by said
detection circuit to interrupt power to an appliance circuit due to
an accidental immersion or the like of an appliance into water or
other conductive liquid, the improvement comprising a fuse line and
an electrically conductive spring physically and electrically
connected through at least one common connection point with said
fuse link and spring being in series and forming a part of said
interruption mechanism for completing a current path in one said
conductor, said fuse link being opened by excessive current through
one of said conductors, said interruption mechanism including
openable means in another of said conductors to complete and open
an electrical path therethrough, said fuse link being electrically
isolated from and mechanically linked to said openable means to
maintain said openable means operative to complete an electrical
path through said other conductor, said openable means being opened
substantially immediately upon opening of said fuse link so that it
no longer maintains said openable means operative to complete an
electrical path through said other conductor.
3. In a power circuit including at least two conductors for
conducting electrical power from a line source via an electrical
shock protection device to an appliance circuit within a housing,
the protection device including an automatic means connected to the
conductors to initiate an overcurrent in response to an immersion
of an appliance circuit in water or other conductive liquid, the
protection device further including interrupting means in at least
one of the conductors responsive to the overcurrent to open the at
least one conductor and interrupt the power circuit in the event of
such immersion, the automatic means including an immersion sensing
conductor and immersion detection circuit to activate the automatic
means to provide the overcurrent by shorting means for establishing
a low resistance shunting of the appliance circuit, the improvement
wherein said immersion sensing conductor and immersion detection
circuit are located in said housing together with the appliance
circuit, an electrical plug housing, said two conductors being
connected between said plug and the appliance circuit, said
interrupting means being located in said plug housing wherein said
interrupting means further includes at least one fuse link and a
spring loaded strip, said fuse link and said strip being physically
and electrically connected through at least one common connection
point.
4. The power circuit of claim 3 wherein said spring loaded strip is
formed of conductive spring material.
5. The power circuit of claim 3 wherein said interrupting means
includes normally open electrical contacts maintained closed to
complete the power circuit in another of the at least two
conductors by said fuse link through a mechanical coupling that
electrically isolates said fuse link from said contacts, said
contacts being released to open upon opening of said fuse link so
that the at least two conductors are opened substantially
simultaneously in response to an immersion of the appliance
circuit.
6. The power circuit of claim 5 wherein said contacts include a
pair of spaced contacts closed by a third bridging contact which is
carried by said spring loaded strip to form double break
contacts.
7. The power circuit of claim 6 wherein said spring loaded strip is
maintained in a position by said fuse link with said bridging
contact in engagement to and between said pair of contacts until
released by the opening of said fuse link.
8. The power circuit of claim 7 in which said pair of contacts,
closed by said bridging contact, applies a force to said bridging
contact when released by said opening of said fuse link which force
is in addition to a force applied to said bridging contact by said
spring loaded strip that is released by the opening of said fuse
link.
9. The power circuit of claim 5 wherein said contacts include a
pair of spaced contacts closed by a third bridging contact which is
carried by said spring loaded strip to form double break
contacts.
10. The power circuit of claim 9 wherein said pair of elongated
strips is curved into a space between said strips.
11. The power circuit of claim 9 further including an insulating
barrier, said pair of elongated strips being self biased toward
each other and maintained in a spaced position by said insulating
barrier located between said strips.
12. The power circuit of claim 3 further comprising a cord set
including a line cord, and plug assembly connected to said line
cord, said interrupting means being included in said plug
assembly.
13. The power circuit of claim 12 further comprising means to
inhibit unwarranted activation of said automatic means by line
transients generated by insertion of said plug into a receptacle
outlet, said means to inhibit including polarization of said plug
by forming its blades in unequal widths and unequal lengths with
the narrower blade, for contacting an ungrounded conductor from
said power source, being longer than the wider blade, for
connecting to a grounded conductor from said power source, whereby
insertion of said plug into a receptacle outlet will cause
connection of said power circuit to an ungrounded conductor prior
to connection to a grounded conductor.
14. The power circuit of claim 12 wherein said line cord is only
two conductors.
15. The power circuit of claim 3 wherein said interrupting means
includes a fuse link connected to a conductive spring strip in
series with said one conductor.
16. In a power circuit including at least two conductors for
conducting electrical power from a line source, via an electrical
shock protection device to an appliance circuit within a housing,
the protection device including an automatic means connected to the
conductors to initiate an overcurrent in response to an immersion
of an appliance circuit in water or other conductive liquid, the
protection device further including interrupting means in at least
one of the conductors responsive to the overcurrent to open the at
least one conductor and interrupt the power circuit in the event of
such immersion, the automatic means including an immersion sensing
conductor and immersion detection circuit to activate the automatic
means to provide the overcurrent by shorting means for establishing
a low resistance shunting of the appliance circuit, said
interrupting means having at least one fuse link in one of said at
least two conductors, said interrupting means further including
normally open electrical contacts which are held closed to complete
the power circuit in another of said at least two conductors, by
said fuse link through a mechanical coupling that electrically
isolates said fuse link from said contacts, said contacts being
released to open upon the opening of said fuse link so that at
least two of said at least two conductors are opened substantially
simultaneously in response to an immersion of said appliance
circuit, the improvement wherein said fuse link is electrically at
one end in series to a conductive spring loaded strip, said
contacts including a third bridging contact and a pair of spaced
contacts closed by said bridging contact which is carried by said
spring loaded strip to form a double break contact arrangement.
17. The power circuit as defined in claim 16 in which said pair of
contacts is made of conductive spring material in the form of a
pair of elongated strips.
18. The power circuit as defined in claim 17 in which said pair of
elongated strips is curved into the spaces between said strips.
19. The power circuit as defined in claim 18 further including an
insulation barrier, said pair of elongated strips being self biased
toward each other but held in a spaced position by said insulating
barrier located between said strips.
20. The power circuit as defined in claim 16 in which said spring
loaded strip is held in a position by said fuse link with said
bridging contact in engagement to and between said contact pair
until released by the opening of said fuse link.
21. The power circuit as defined in claim 20 in which said pair of
contacts, closed by said bridging contact applies a force to said
bridging contact when released by the opening of said fuse link
that is in addition to the force applied by said spring loaded
strip that is released by the opening of the fuse link.
22. In a power circuit including at leas two conductors for
conducting electrical power from a line source via an electrical
shock protection device to an appliance circuit located within a
housing, the protection device including an automatic means
connected to the conductors to initiate an overcurrent in response
to an immersion of an appliance circuit in water or other
conductive liquid, the protection device further including
interrupting means in at least one of the conductors responsive to
the overcurrent to open the at least one conductor and interrupt
the power circuit in the event of such immersion, the automatic
means including an immersion sensing conductor and immersion
detection circuit to activate the automatic means to provide the
overcurrent by shorting means for establishing a low resistance
shunting of the appliance circuit, the improvement wherein said
interrupting means includes at least one fuse link, said fuse link
being physically and electrically connected at one end via a
conductive spring loaded strip in electrical series with at least
one conductor.
23. The power circuit of claim 22 wherein said interrupting means
is located in a plug assembly of a line cord set which also
includes a line cord between said plug assembly and the appliance
circuit located within said housing.
24. The power circuit as defined in claim 23, in which said
immersion sensing conductor and said detection circuit are located
in said plug assembly, together with said interrupting means and in
which said sensing conductor is extended from said plug assembly to
said appliance circuit as an additional conductor in said line
cord.
25. The power circuit as defined in claim 23, in which said
improvement further includes means to inhibit unwarranted
activation of said automatic means by line transients generated at
the time said plug is inserted into a receptacle outlet, said means
to inhibit including the polarization of said of said plug by
forming said blades in unequal widths and also including forming
then in unequal lengths with the narrower blade, for contacting an
ungrounded conductor from said power source, being longer than the
wider blade, for connecting to a grounded conductor from said power
source so that insertion of said plug into a receptacle outlet will
cause connection of said power circuit to an ungrounded conductor
prior to connection to a grounded conductor.
26. The power circuit of claim 22 wherein said immersion sensing
conductor and immersion detection circuit are located in said
housing.
27. The power circuit of claim 22 wherein said immersion sensing
conductor and said immersion detection circuit are located in said
plug assembly together with said interrupting means, and wherein
said sensing conductor is a single conductor extended from said
plug assembly to said appliance circuit as an additional conductor
in said line cord.
28. The power circuit as defined in claim 22 in which said
interrupting means includes normally open electrical contacts which
are held by closed to complete the power circuit in another of said
at least two conductors, by the said fuse link through a mechanical
coupling that electrically isolates said fuse link from said
contacts, said contacts being released to open upon the opening of
the fuse link so that at least two of said at least two conductors
are opened substantially simultaneously in response to an immersion
of said appliance circuit.
29. The power circuit as defined in claim 28, in which said
immersion sensing conductor and detection circuit are located in
said housing together with said appliance circuit.
30. The power circuit as defined in claim 28 further comprising a
cord set including a line cord, and plug assembly connected to said
line cord, said interrupting means being included in said plug
assembly.
31. The power circuit as defined in claim 22 in which said shorting
means includes means to inhibit triggering of said thyristor by
transient conditions other than immersion of said appliance
circuit.
32. The power circuit as defined in claim 31 in which said means to
inhibit triggering includes a capacitor connected in parallel with
said thyristor.
Description
BACKGROUND OF THE INVENTION
With the ever increasing use of electrical power in the home, there
is a growing governmental and public awareness of electrical shock
hazard and recognition of the need for improved means to reduce or
eliminate the possibility of harmful electrical shock. This has
resulted in a mandating of more sophisticated protection, requiring
use of means considered most effective, but within the restricting
framework of cost that affects the matter of practical
implementation.
If one can never presume to place a price on human life, the cost
of protecting it should not be a factor, but it is one that is
constantly at work in the marketplace. Maximum electrical shock
protection should ideally be provided in all instances, but there
is a demonstrated willingness to accept risk in the interest of
economy and especially to forego safety modifications that might
escalate the price of less expensive items. The cost of adding
ground fault and line-to-line protection to hairdryers is more
acceptable than when added to hair curlers, where the cost of the
protection may well exceed the basic cost of the appliance yet the
curler can be as dangerous as the dryer.
These examples were selected because conditions of greatest
electrical shock hazard have been generally established to exist
wherever appliances are used around water, but most particularly in
the bathroom where intensive use of electrical appliances is
combined with extreme proximity to water under widely variable
conditions, many of which include a ready opportunity for complete
or partial immersion, It thus appeared that a simple yet effective
device which needed only to interrupt power to the appliance in the
event of its immersion could provide shock protection in a majority
of hazardous instances and might be produced at lower cost than,
for example, those described in my U.S. Pats. No. 3,997,818 and
4,707,759, which are designed to protect under a very broad
spectrum of hazardous conditions.
While many immersion detection circuit interrupter devices have
been designed and marketed, it is believed that the present
invention more closely approaches the goal of providing maximum
effectiveness with minimum cost in order to achieve the most
extensive use. The expense of electromagnetic switching devices is
avoided, and where solid state devices are employed, their closed
mode of failure is made to represent a positive fail-safe factor
rather than a negative consideration in the matter of protective
functioning. The present invention is particularly rapid in its
protection due to a shorting technique which diverts current from
the appliance circuit through a low resistance path as it activates
the permanent interruption device. It uses very few electronic
components and has a simplified construction which is due in part
to its single service design. While accidental immersion of an
electrical appliance is included in the most hazardous of shock
scenarios, such scenarios may be expected to be extremely rare in
the course of normal human experience and the expense of making a
protective device resettable would appear to be not only
superfluous but counterproductive in the attempt to minimize cost,
unless a device is prone to the annoyance of unwarranted
interruption and thus has a particular need to be made resettable.
Safeguards against unwarranted interruption are provided in the
present invention and the fast acting fuse link in the interrupter
mechanism typically has a current rating far below that of the
standard overcurrent devices installed for the protection of branch
circuits so that the shorting technique does not result in an
interruption of the branch service. However, the rarity of an
immersion mishap should prevent such a branch interruption from
being considered an aggravation and fuse links designed to permit
use with appliances having greater current demands may become
permissible.
SUMMARY OF THE INVENTION
In one aspect, this invention is seen to comprise a power circuit
having at least two conductors for conducting electrical power from
a line source to an appliance circuit, within an appliance housing,
and having an electrical shock protection device. The improvement
in the device includes an automatic means connected to the
conductors to initiate an overcurrent in response to an immersion
of the appliance circuit in water or other conductive liquid. The
power circuit also includes interrupting means, in at least one of
the conductors, that is responsive to the overcurrent to open the
one conductor and interrupt the power circuit in event of such
immersion.
In other aspects, the automatic means is employed to initiate the
overcurrent and includes a sensing conductor and immersion
detection circuit. The automatic means provides the overcurrent by
establishing a short or low resistance shunting of the appliance
circuit. The interrupting means in the conductors has at least one
fuse link in one of the at least two conductors.
Preferably, the interrupting means includes normally open
electrical contacts which are held closed to complete the power
circuit in another of the at least two conductors, by the fuse link
through a mechanical coupling that electrically isolates the fuse
link from the contacts. The contacts are released to open upon the
opening of the fuse link so that at least two of the at least two
conductors are opened substantially simultaneously in response to
an immersion of the appliance circuit.
An object of this invention is to provide an especially rapid
immersion detection and power interrupting shock protective
response in a device that can be made an integral part of appliance
design.
Another object is to provide an improved immersion detection
circuit interrupter (IDCI) that can be produced at minimal cost in
order to make such integral shock protection, in the event of
immersion, more generally acceptable to the maker, seller and
purchaser.
Still another object is to provide a circuit interrupter in a
compact package, so that design factors will not be a reasonable
argument against acceptance of its integral shock protection by
maker, seller or purchaser.
An additional object is to provide an immersion detection circuit
interrupter that will function over a wide range of input voltages
and frequencies so that the same type of device may enjoy wider
usage.
A further object is to provide an immersion detection circuit
interrupter device that is not reduced in protective function by
the plug of the cord set being inserted into a receptacle outlet
having its ungrounded and grounded neutral connections
reversed.
A still further object is to provide an immersion detection circuit
interrupter that is resistive to the effects of both physical abuse
and transient electrical conditions that might cause an unwarranted
power interruption.
One more object is to provide an immersion detection circuit
interrupter with a mode of failure that leaves an appliance safe to
handle, in the event of protective failure, and incapable of being
used when no protection can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention, both as to its organization and principles of
operation, together with further objects and advantages thereof,
may be better understood by reference to the following detailed
description of the embodiment of the invention taken in conjunction
with the accompanying drawings in which:
FIG. 1 is a schematic diagram showing the sensor conductor and the
immersion detection circuit located in the appliance housing as
part of the appliance circuit and the interrupting device located
in the plug assembly.
FIG. 2 is a schematic diagram showing the immersion detection
circuit located in the plug assembly with the interrupting device
and the sensor conductor extended to the appliance circuit as a
third conductor in the line cord.
FIG. 3 is an exploded view of the interrupter device contained in
the plug assembly.
FIG. 4 and FIG. 5 are opposite side views and FIG. 6 is an end view
of the same interrupter device.
FIG. 7 and FIG. 8 are side and end views respectively, of the plug
housing that contains the interrupter device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to the schematic diagrams of FIG. 1 and FIG. 2, it
may be seen that power is supplied from line source 50 through
ungrounded conductor 51 and grounded neutral conductor 52 and their
respective receptacle terminals 53 and 54 to respective plug blades
3 and 2. From ungrounded plug blade 3 to the appliance load 58
contained in appliance housing 56, the current path may be seen to
include a fuse link 27, a spring support strip 4 to which the link
is attached, conductor 17 of line cord 15 and appliance switch 57.
From grounded neutral plug blade 2 the current path to the
appliance load 58 may be seen to include spring contact strips 10
and 11 connected by bridging contact 5 which is carried on the end
of fuse support strip 4 but is electrically isolated from it by
insulating sleeve 6. From spring contact strip 11 the path
continues to appliance load 58 through conductor 16 of line cord
15.
It may also be seen that the detection circuit in both FIG. 1 and
FIG. 2 includes a full-wave rectifier 59 which has its a.c. input
terminals connected across conductors 16 and 17 so as to be
connected in parallel with appliance load 58 together with its
controlling switch 57.
Thyristor 60, shown as a silicon controlled rectifier (SCR), is
connected across the output terminals of full-wave rectifier 59 so
as to pass output current from the rectifier when triggered and
placed in a forward conductive state. The full-wave rectifier 59
together with the thyristor 60 will thus pass current in either
direction between ungrounded conductor 17 and grounded neutral
conductor 16 to shunt or divert current away from appliance load 58
and its switch 57, to short circuit the power path and create an
overcurrent which opens the fuse link of the interrupter and
releases the bridging contact to interrupt electrical connection to
both the ungrounded and grounded neutral sides of the line.
Triggering of the thyristor 60, by immersion, is accomplished
through sensor conductor 62 which is connected to the gate of the
thyristor, either directly or through optional current limiting
resistance 63. When a small current is caused to pass between the
sensor conductor and current carrying parts of the appliance or
between the sensor conductor and earth ground, as by the connecting
contact of water or other conductive medium, the thyristor 60 is
triggered and creates the short circuit of the power circuit that
activates the interrupter.
Capacitor 61 is connected in parallel with thyristor 60 as a
primary means of inhibiting unwarranted triggering of the thyristor
by line transients, supplying a small forward conditioning current.
It is connected in a filter capacitor position but employs values
far lower than those used for filtering purposes. 0.47 to 1.0 mfd
is sufficient and values above 2.0 mfd are generally not desirable.
Values as low as 0.1 perform efficiently once the plug is inserted
in its receptacle and the capacitor becomes charged, but the larger
values are needed to increase triggering resistance to the waveform
spike often generated when the plug is inserted. An additional
method of inhibiting unwarranted triggering, by switching spikes
and the like, involves plug blade structure and will be discussed
with reference to the mechanical drawings.
Selection of gate sensitivity is also of prime importance in the
avoidance of unwarranted triggering of thyristor 60. The Igt should
be in excess of 200 microamperes and preferably above 1
milliampere.
Where especially compact circuits are desired the thyristor is
typically a 0.8 ampere SCR in a TO-92 package with an insensitive
gate. The full-wave rectifier is rated at 1.5 amperes. While these
should be considered sacrificial, the fuse action is fast and the
rectifier may often survive. In circuits using components with
higher surge ratings both components may survive, although the
interrupter is not intended for reuse.
Referring now to FIG. 3, we see an exploded view of the interrupter
as contained in a prototype plug and we can more readily see how
the ring shaped bridging contact 5 is carried at the end of the
fuse link supporting spring strip 4, while being electrically
isolated from it by insulating sleeve 6. This spring strip, as well
as spring strips 10 and 11 are preferably formed of tempered
beryllium copper. The base of spring strip 4 is secured in post 7
which is mounted in the interrupter body 1 so that terminal screw
24 can be used to attach line cord conductor 17.
One end of the fuse link 27 is secured, preferably by soldering, to
the spring strip 4, which not only connects fuse link 27 to line
cord conductor 17 but applies a small amount of tension to the link
once its other end has been properly attached to the base of plug
blade 3 by using terminal screw 25 or by clamping in slot 26. Plug
blade 3 is the narrower of the two blades 2 and 3 and is designed
for contact with the ungrounded side of the line in a polarized
receptacle.
Spring contact strip 10 has its support post 8 connected directly
to plug blade 2 which is the wider one and intended for connection
to the grounded neutral side of the line in a polarized receptacle
outlet. Oppositely curving spring strip 11 is connected to
conductor 16 of the line cord 15 through its support post 9 and
terminal screw 23. Strips 10 and 11 connect the grounded neutral
side of the line to the load when bridging contact 5 is held in
position by spring strip 4 which is retained by fuse link 27.
Strips 10 and 11 have much less curve in the unstressed condition
shown in FIG. 3, but are prestressed by curving them further and
inserting them in interrupter body 1 where their free ends press
against insulative spacing barrier 18 which separates them. While
the prestressed degree of curvature, shown in FIGS. 4 and 5, could
be provided in unstressed strips, prestressing against the barrier
assures a development of high contact pressure with less movement
of the bridging contact and also helps assure a positive
positioning of the strips.
The nature of the interaction between the strips 10 and 11 is such
that insertion of the bridging contact between them is resisted by
a force that is initially great and subsequently diminished.
Conversely, once the contact is fully inserted, the force of
ejection exerted on the bridging contact is small and becomes
subsequently greater as it is ejected. As contact 5 is inserted
further, a point can be reached in which ejection force approaches
zero. At or near this point, the fuse supporting strip can maintain
the connecting position of the contact it carries without adverse
additive effect on the tension of the fuse wire. Insertion of the
bridging contact beyond this point can result in the development of
force in a direction that tends to resist rather than assist in its
removal. The spacing barrier 18 that separates the ends of the
inwardly curving strips is also positioned to act as a stop for
bridging contact 5 and prevent excessive insertion.
As a matter of convenience in assembly, final connection of the
fuse link 27 to plug blade 3 is not made until bridging contact 5
has been properly pressed into position between the oppositely and
inwardly curving strips 10 and 11,thus bringing fuse link
supporting strip 4 into a proper position. The bridging contact is
then held against its positioning stop 18, fuse link 27 is lightly
pulled to straighten it, and then it is fastened to blade 3,
preferably by clamping in slot 26, while exerting only enough
tension to eliminate a curvature in the link which could affect its
rating.
when the fuse link 27 opens the ungrounded side of the line, its
supporting spring strip 4 is released and urges the ejection of the
bridging contact 5 from the space between curving strips 10 and 11
to open the other side of the line. As the bridging contact 5 is
urged toward ejection, by the released link supporting spring strip
4, additional force of ejection is applied by the inwardly curving
spring contact strips 10 and 11 in a rapidly increasing amount so
that ejection can appear almost explosive in nature. Since the
curving strips 10 and 11 and bridging contact 5 also comprise a
double break contact arrangement, interruption of current is
enhanced.
Close attention should be given to design of the interrupter body 1
to assure that the fuse link 27 is well contained in a shielding
and insulating compartment that can also safely direct any escaping
material, since the link will more often vaporize than separate and
brief but strong arcing between elements of opposite polarity can
often occur in the vaporizing metal if short paths are made
available.
The mechanical components 4, 5, 6, 10 and 11 which could apply
strain to fuse link 27 have low inertial qualities that contribute
to the interrupter's resistance to premature rupture of the fuse
link that might be caused by dropping the plug on a hard surface or
other such physical abuse.
FIG. 4 and FIG. 5 show opposite side views and FIG. 6 shows an end
view of the interrupter shown in FIG. 3.
FIG. 7 shows a side view and FIG. 8 shows an end view of plug
housing or enclosure 12 with its removable back cover 13 that is
made to extend beyond the housing to form a convenient plug-pulling
finger grip, and also shows strain relief 14 for line cord 15.
In FIGS. 3, 4, 5 and 7 it can be noted that the plug blades are of
the unequal width required for polarizing, but also that they are
of unequal length, a simple modification that appears to be useful
in avoiding unwarranted interruptions.
I have noted, while testing for resistance of the invention to
unwarranted interruption, and using a sensitive SCR without the
capacitor protection to achieve a "worst case" condition, that
breaking and remaking the power connection on the ungrounded side
of the line while the grounded neutral side remained connected,
causes triggering of the SCR with far greater frequency than when
the arrangement is reversed. When making and breaking the power
connection on the grounded side while the ungrounded side remained
connected, triggering was very seldom. This effect is apparently
due to a component conditioning effect resulting from the feeble
currents created by an earth ground capacitance.
The longer blade 3 (just below the maximum allowable length),
contacts the ungrounded side of the line and enables the power
circuit to be energized with respect to the earth ground
capacitance effect just prior to the contact of the shorter blade 2
(just above the minimum allowable length), with the grounded
neutral side of the line which completes the power circuit. While
the time differential is small it appears to be effective in most
test instances.
Even if marginal in reliability due to uncontrollable variables,
such as speed of plug insertion, it is a plus factor that can
enhance the other means and can be included at zero or near zero
cost.
While this invention has been described with respect to certain
specific embodiments, it will be appreciated that many
modifications and changes may be made by those skilled in the art
without departing from the inventive concepts or spirit of the
invention. It is intended therefore, by the appended claims, to
cover all such modifications and changes as fall within the true
scope of the invention.
* * * * *